1. Field of the Invention
The present invention generally relates to a misfire detecting apparatus for an internal combustion engine. More specifically, the invention is concerned with a misfire detecting apparatus for detecting occurrence of misfire events or phenomenon in an internal combustion engine due to abnormality in the operation of an ignition or firing system, a fuel system and others.
2. Description of the Related Art
As a misfire detecting apparatus for the internal combustion engine (also referred to simply as the engine) known heretofore, there may be mentioned one which is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 41400/1990 (JP-A-H2-41400). According to this known apparatus, a rotation speed (rpm) of the engine is monitored by using a crank angle sensor, wherein occurrence of misfire is determined on the basis of variation in the engine rotation speed (rpm) which is brought about by the misfire. More specifically, in the conventional misfire detecting apparatus, first and second predetermined angular intervals or ranges are, respectively, defined before and after a predetermined angular position of a crank shaft which serves as a reference position, wherein a ratio (time ratio) between the times taken for the crank shaft to rotate through the first and second intervals, respectively, is determined by a so-called time ratio detecting means on the basis of the output signal of the crank angle sensor. Subsequently, from the time ratio thus determined, acceleration (conceptually encompassing deceleration) is determined. By comparing the acceleration with a predetermined value which indicates occurrence of misfire event, decision is made as to whether or not misfire has taken place.
The misfire detecting apparatus known heretofore is however disadvantageous in that it lacks the capability of discriminating an intermittent occurrence of misfire and a successive or continuous occurrence thereof from each other. Consequently, when the situation under which the misfire occurs changes or when the rotation speed of the engine varies under the influence of vibration of a motor vehicle transmitted from the wheels in the course of running on a bad or rough road, there arises a possibility that erroneous misfire decision may be resulted. In reality, when the motor vehicle is driven on a rough road, the engine experiences significant variation in the rotation speed, which may lead to erroneous decision that the misfire takes place regardless of the absence thereof in actuality. Besides, the misfire decision is susceptible to adverse influence when the engine rotation speed and/or engine load changes. Under the circumstances, there exists a great demand for the misfire detecting apparatus for the internal combustion engine which can detect the occurrence of misfire without fail and thus ensure high reliability for the misfire detection.